Based on what I've read, the runtime error "no class def found" means that the app is trying to use a class that isn't supported by the phone's Java runtime. In other words the app is incompatible with the phone.

It's not fixable except by rewriting the app to not use the class that's missing. Only the original developer or another developer with access to the app's source code can do that and they would probably need access to the phone model that's giving the error for debugging purposes.